BrewCalc

Yeast Pitch Rate Calculator

How much yeast does this batch need?

Batch Volume (L)

Original Gravity

Pitch Rate (M cells/mL/°P)

Billion Cells per Pack

Yeast Packs Needed

1.88

0.75 M cells/mL/°P suits most ales; double it for lagers.

Cells Required: 188 billion
Wort Gravity: 12.5 °P

What you entered

Batch Volume (L): 20Original Gravity: 1.05Pitch Rate (M cells/mL/°P): 0.75Billion Cells per Pack: 100

1
Convert gravity to degrees Plato
(1.05 - 1) x 1000 / 4= 12.5 deg P
2
Cells required (million cells/mL/deg P)
0.75 x 20,000 mL x 12.5= 187,500 million
3
In billions of cells
187,500 / 1000= 187.5 billion
4
Packs of yeast needed
187.5 / 100 billion per pack= 1.875

Result

Yeast Packs Needed: 1.88

Yeast cells needed by batch size and gravity

Pitch rate is measured in million cells per millilitre per degree Plato. Ales use about 0.75, lagers about 1.5. Rows assume 100 billion cells per pack.

Batch	Original gravity	Degrees Plato	Pitch rate	Cells needed	Packs
23 L	1.048	12.0	0.75 (ale)	207.0 billion	2.07
20 L	1.050	12.5	0.75 (ale)	187.5 billion	1.88
20 L	1.060	15.0	0.75 (ale)	225.0 billion	2.25
20 L	1.080	20.0	1.0	400.0 billion	4.00
20 L	1.050	12.5	1.5 (lager)	375.0 billion	3.75
40 L	1.050	12.5	0.75 (ale)	375.0 billion	3.75

Underpitching stresses the yeast and produces off flavours; a big beer or a lager can need three or four packs, which is why most brewers make a starter instead. A single fresh pack holds roughly 100 billion viable cells and loses about 20% a month.

Ales and lagers need different rates

The usual target is 0.75 million cells per millilitre per degree Plato for ales and about double that for lagers, because cold fermentation slows reproduction. Under-pitching a lager is one of the most common causes of sluggish, off-flavoured fermentation.

Why under-pitching shows up in the glass

Too few cells forces the yeast through extra growth cycles before fermentation proper, and that stress produces esters, fusel alcohols, and diacetyl. Pitching enough healthy yeast is the cheapest quality improvement available to a homebrewer.

Frequently asked questions

I'm brewing a 5-gallon lager at OG 1.060 — how many yeast packs do I need?

At the standard lager rate of 1.5 million cells/mL/Plato, a 19-liter batch at ~15 Plato needs about 427 billion cells. A fresh liquid pack has ~100 billion cells, so you'd need about 4 packs — or make a 2-liter starter from 1-2 packs.

How is the pitch rate calculator different from the ABV calculator?

The pitch rate calculator is a pre-fermentation tool — it tells you how much yeast to add before you brew. The ABV calculator is post-fermentation — it measures the alcohol produced from the gravity drop after the yeast has done its work.

Does yeast age matter for pitch rate?

Yes, significantly. Liquid yeast viability drops about 20% per month at fridge temperature. A 3-month-old pack might have only 50 billion viable cells instead of 100 billion, effectively halving your pitch rate. Always check the production date.